FIG. 1 shows a conventional data transceiver system disclosed in Japanese patent application laid-open No. 11-331234. In the data transceiver system, a radio terminal unit conducts data transmission and reception to and from an application server as follows. The radio terminal unit or base station notifies a gateway server of circuit conditions in a radio section, and the gateway server adjusts parameters such as packet length and retransmission duration when converting to a radio protocol, thereby carrying out the data communication.
The conventional data communication system disclosed in Japanese patent application laid-open No. 11-331234 transmits data after the gateway converts into the radio network protocol using parameters (packet length, retransmission timer, and window size) suitable for the circuit conditions of the radio network.
In an ordinary video and audio multimedia communication, however, there are different level protocols: a lower level protocol different on the radio and the Internet sections; and a higher level protocol common to the radio and the Internet sections for enabling streaming communication. The foregoing conventional data communication system enables transmission and reception according to the parameters matching to the error characteristics of the networks according to only the lower level protocols, thereby being unable to conduct the transmission at an appropriate packet length according to the higher level protocol.
The present invention is implemented to solve the foregoing problem. Therefore it is an object of the present invention to provide a data transmitter, gateway, data transceiver and data communication method capable of reducing the fraction of packets lost by receiving data at a packet length adaptable to the error conditions of the networks even according to the common higher level protocol.